Under this system, your alignment matches the Plane that you are most closely associated with. Essentially "Alignment" becomes a kind of citizenship that you have with another plane of existence.

Rather than having a Moral and Ethical component of your alignment (i.e., Lawful Good, Chaotic Neutral, Neutral Evil), you instead have an adjective based on a plane (Celestian, Giant Frog, Carcerian).

Actions no longer directly dictate alignment. A Celestian character who consistently violates the principles of Mount Celestia earns punishment in the afterlife but does not risk involuntary alignment change. Such a character may still choose to convert to a plane that will reward them for those acts instead, or have the future ownership of their soul transferred behind their back.

Your alignment is no longer simply the intersection of two arbitrary ideas you hold (Law and Chaos, which don't mean anything at all, and Good and Evil, which are almost as badly defined), but instead gives you a distinct moral philosophy.

Your afterlife is always in the plane you are aligned with. You don't have three possible planes where you might end up in any of them.

Alignment requirements change under this for a few classes. Clerics, for instance are always aligned with their Deity's home plane by definition. They may not always uphold all of the principles that the plane demands, but as long as they are in good standing with their deity, they are aligned with that plane. Piously following a religion can, likewise, make you more aligned with the deity's home plane, if the deity doesn't think badly of you.

Detect spells detect people who are aligned with certain groups of planes, simply enough. Any plane with the Minor or Major aligned trait is picked up on a Detect spell. Optionally, Acheron and Pandemonium may also be counted as Evil, Gehenna and Bitopia Lawful, Carceri and the Beastlands Chaotic, and Arcadia and Ysgard Good, possibly at reduced aura strength.

This variant can be extended to allow alignments for the Inner planes: Air, Earth, Fire, Negative, Positive, and Water. Under this system, Undead are almost invariably aligned with the Negative Energy Plane. Animals and beings of the Elemental planes have Elemental alignments usually, as do Druids.

The Energy Planes may or may not detect as Outer Planar Alignments. In such a case, the Negative Energy Plane detects as Evil and the Positive plane detects as Good. The Elemental planes are invariably neutral with regards to Detect spells.

Casting a spell with an alignment descriptor may or may not be an intrinsically aligned act under this variant. Whether it is or not is a question left to the DM on implementation. How it is aligned depends on the spell.

With the Inner Planar variants, casting spells with Elemental descriptors is also an aligned act; a spellcaster who makes a habit of using [Fire] spells has a good chance of having a Fire alignment.

This has been written before by a number of writers over the years, few of whom had the same ideas as each other, or fully understood each other, so what we have now is a contradictory mess. Add on that the moral systems most games are most interested in understanding (those the PCs subscribe to) have little to attach to, as the Upper Planes have been little detailed, since you don't go there to kill things, and this quickly becomes the largest part of the project.

Celestians, and the followers of their moral philosophies, believe in a universal law that would, if universally followed, benefit everyone. Further, they believe this law to be intrinsically good; its benefit flows from its being intrinsically good, but it should be followed in all cases even if it only gives benefits in a few (even if compared to inaction).

The fine points of this universal law are debated by Celestian scholars, but with the amount of time and archon-hours put into this (anywhere from thousands of years and billions of hours to an infinite amount of both, depending on whether a sensible arrangement of the planes is used or an infinity is thrown at the problem), the foundations are solid enough that mortals wouldn't be able to make a counterpoint that hasn't already been debated endlessly (possibly literally). The records of these debates would, and do, fill several good size libraries even when compressed through abuse of the Secret Page spell; although the fundamental principles are simple enough to explain (not to harm, essentially, so no murder, no stealing, and so on), the applications are complex.

This has real consequences in its application to mortal affairs. While still generally good (that is, they keep Fiends, Illithids, and the like from destroying your home), Celestians see absolutely no problem with a land being ruled by far-away or unresponsive rulers, and are wary of social progressive movements, for instance. After all, if the Law is invariant throughout the universe, then whether it is being executed under the authority of one close to home or far away is irrelevant. Likewise, the concerns of the people pale in importance next to the value of this universal Law. Social progress is suspicious because the Law is not only the same everywhere, but at every time; a society that obeys the Law clearly, then, has no need of social progress. Advancements, sometimes even as simple as the abolition of literal second-class citizenship, are often stalled by debating whether or not the advancement is demanded by the Law.

Bitopians believe that people benefit best by separating out into their compatible and natural societies, having little interaction with others on a personal level, and peaceful coexistence and mutual defense on a societal level. Thus, in a Bitopian utopia, there would be a Gnomish town and a human town and an elven town and a goblin town, but no combined settlements except possibly big cities that segregate at the district level.

Bitopians, therefore, will ride to the rescue of a tribe of goblins that is at risk of being destroyed to sacrifice to a demon, but if their society then takes the refugees in as cheap labor and the goblins then petition for rights as citizens they will oppose it, having been fighting to keep the goblins separated from day 1.

Empty Placeholder. Morality of the Negative Energy Plane depends on whether you use Crawling Darkness or Playing with Fire. Whichever you use, it wants you to act like you're undead, and the Positive Energy Plane is in favor of spreading life.